Metal nitrides and/or metal carbides with nanocrystalline grain structure

ABSTRACT

Disclosed is a composition having nanoparticles or particles of a refractory metal, a refractory metal hydride, a refractory metal carbide, a refractory metal nitride, or a refractory metal boride, an organic compound consisting of carbon and hydrogen, and a nitrogenous compound consisting of carbon, nitrogen, and hydrogen. The composition, optionally containing the nitrogenous compound, is milled, cured to form a thermoset, compacted into a geometric shape, and heated in a nitrogen atmosphere at a temperature that forms a nanoparticle composition comprising nanoparticles of metal nitride and optionally metal carbide. The nanoparticles have a uniform distribution of the nitride or carbide.

This application claims the benefit of U.S. Provisional Application No.62/620,596, filed on Jan. 23, 2018. The provisional application and allother publications and patent documents referred to throughout thisnonprovisional application are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure is generally related to structure and synthesisof metal carbides and metal nitrides.

DESCRIPTION OF RELATED ART

Refractory transition metal carbides and nitrides have the highest knownmelting points (2600-3900° C.) out of all engineering materials. Theyalso offer outstanding hardness, chemical inertness, wear resistance,electrocatalytic activity, electrical and thermal conductivity, and bothionizing and non-ionizing (neutron) absorption. Refractory metalcarbides are typically prepared by powder metallurgy methods such as hotpress sintering. Ordinarily, these techniques, which are both energy-and time-intensive, yield metal carbide ceramic composites that have alarge granular structure, broad ceramic particle and grain sizedistribution, and are, subsequently, brittle. Powdered metal nitridescan be produced from metal particles in a flow of nitrogen but have tobe formulated into shaped components under pressure and hightemperatures. Films, fibers, and powders of these ceramics have beenmade from polymeric precursors, but neither polymer-derived ceramics norreactive melt infiltration processes yield dense, pure, monolithic, andnanocrystalline metal carbides or metal nitrides.

Since the late 1960s, there has been an interest in ceramic materialsthat withstand high temperatures and exhibit high mechanical hardness.Their use includes, but is not limited to, applications such as toolsfor grinding/machining, ball bearings, armor components, reinforcementfibers and fillers (integrated in other materials), and turbine bladesof vehicles and aircraft. However, to date, materials have found nosuccess in structural applications, due to their brittleness, weaknessin shear and tension, and poor shock resistance. More recently, therehas been a resurgence of interest in ultra-high temperature materialsfor high-speed air and space vehicles. These vehicles, which includeboth single-use (expendable) and multi-use (reusable) systems, includemanned and unmanned platforms that travel through various layers ofatmosphere and/or space, and include a propulsion system (such as anair-breathing engine and/or a rocket motor) and/or are unpowered. Thesevehicles operate at sufficiently high velocities to generate high heat(in excess of 2,200° C.) and potential ablation degradation problems forleading edges and nose tips along with any propulsion system components.In order to offer reliable and durable performance, engine componentsmust meet several requirements: high melting temperature, high strength,well-defined thermal conductivity, and ablation and environmentalresistance (oxidative resistance). Successful large-scale implementationof these high-performance engineering solutions is contingent on thedevelopment of appropriate materials that can be easily processed intoshaped components with the required thermomechanical and thermochemicaldemands and maintain their exceptional properties without active coolingsystems at temperatures greater than 2,200° C. The refractoryinterstitial transition metal carbides are extremely hard and resistchemical, oxidative, ablative, or thermal damage. Unfortunately, theyare also brittle and difficult to machine. Currently, there is nomaterials engineering and manufacturing solution to these limitations.However, an inexpensive method to manufacture these ceramics willprovide materials that withstand extreme mechanical and thermalconditions and will afford tough shaped components.

Beyond high-temperature engineering applications, a current interestexists to develop metal carbides and metal nitrides with small particlesizes and high surface areas to function as catalysts or catalyticsupports. Nanostructured tungsten carbide (WC) and iron nitride (Fe₃N)are promising examples. Selected metal carbides and nitrides, such as WCand Fe₃N, offer high catalytic efficiencies that compete with Pt/Pd/Ru,but are a much less expensive and more durable material alternative.Since they offer high thermal stability and chemical inertness, theywithstand chemical reactions (driven by high temperature orelectropotential) and retain high surface areas without catalystpoisoning, coarsening, or dissolution. These materials show promise inthe anodes of direct methanol fuel cells (DMFC), which oxidize methanoland electrochemically split water. Strong chemisorption of CO on thenoble metals makes these electrocatalysts susceptible to CO poisoning,blocking the active site for methanol oxidation. Consequently, thediscovery of less expensive catalysts such as WC, which resists loss ofits surface area to CO, facilitates large-scale commercialization ofDMFCs. Other similar metal carbides and nitrides, such as tungstennitride (W2N) and vanadium nitride (VN), have shown promise in methanecarburization, pyridine hydrodenitrogenation, and oilier industrialprocesses.

BRIEF SUMMARY

Disclosed herein is a composition comprising: nanoparticles of arefractory-metal carbide and, optionally, nanoparticles of arefractory-metal nitride. The nanoparticles have a uniform distributionof the carbide or nitride.

Also disclosed herein is a composition comprising: a metal componentselected from: nanoparticles or particles of a refractory metal, arefractory metal hydride, a refractory metal carbide, a refractory metalnitride, or a refractory metal boride, an organic compound consisting ofcarbon and hydrogen, and a nitrogenous compound consisting of carbon,nitrogen, and hydrogen.

Also disclosed herein is a method comprising: providing a precursorcomposition comprising: a metal component selected from: nanoparticlesor particles of a refractory metal, or a refractory metal hydride; anorganic compound consisting of carbon and hydrogen; and optionally anitrogenous compound consisting of carbon, nitrogen, and hydrogen;milling the precursor composition; curing the precursor composition toform a thermoset composition; milling the thermoset composition; andheating the thermoset composition in an inert atmosphere at atemperature that forms a nanoparticle composition comprisingnanoparticles of carbide of the refractory metal and optionally anitride of the refractory metal.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation will be readily obtained by reference tothe following Description of the Example Embodiments and theaccompanying drawings.

FIG. 1 schematically illustrates a process for forming the disclosedcompositions.

FIG. 2 schematically illustrates particles 10 embedded in a thermosetmatrix.

FIG. 3 schematically illustrates the transfer 40 of carbon atoms fromthe carbon matrix 30 to the nanoparticle 50.

FIG. 4 schematically illustrates nanoparticles 50 and inclusions 60 in acarbonaceous matrix 70.

FIG. 5 shows X-ray diffraction (XRD) plots of ceramics synthesized fromdifferent metal precursors

FIG. 6 shows thermogravimetric analysis of a reaction of metal andpolymeric precursors.

FIG. 7 shows a Scanning Electron Microscopy (SEM) image ofmicrostructure of ceramics

FIG. 8 shows XRD plots of ceramics.

FIG. 9 shows a photograph of a metal nitride ceramic monolith.

FIG. 10 shows a photograph of a metal nitride ceramic monolith.

FIG. 11 shows an XRD plot of a metal nitride ceramic.

FIG. 12 shows thermogravimetric analysis of a reaction of metal andpolymeric precursors

FIG. 13 shows an XRD plot of a metal nitride ceramic.

FIG. 14 shows an SEM image of microstructure of ceramics

FIG. 15 shows an SEM image of microstructure of ceramics

FIG. 16 shows an XRD plot of a metal nitride ceramic.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

In the following description, for purposes of explanation and notlimitation, specific details are set forth in order to provide athorough understanding of the present disclosure. However, it will beapparent to one skilled in the art that the present subject matter maybe practiced in other embodiments that depart from these specificdetails. In other instances, detailed descriptions of well-known methodsand devices are omitted so as to not obscure the present disclosure withunnecessary detail.

This disclosure concerns a method for in situ synthesis of purenanoparticulate refractory metal nitrides and/or metal carbides withnanocrystalline grain structure. The method uses Group IV-VI metals andembeds them within a carbon matrix. The synthesis method uses nitrogenand/or argon atmospheres in a two-step process that, depending oncustomizable reaction methods, yields either a shaped ceramic compositemonolith with structural integrity or a micropowder with the samecomposition. The synthesis method allows control over the crystallitegrain size, density, shape, mechanical properties, hardness, magneticsusceptibility, and electrical/thermal conductivity. The material isdesigned for various engineering applications and can withstandtemperatures up to and in excess of 3000° C.

Refractory metal carbide and nitride ceramics offer higher meltingpoints (>3000° C.) than any other engineering materials. In order tosynthesize ceramic components and dense shapes, the fabrication processsubjects transition metal carbide/nitride powders to hot presssintering, which requires extremely high pressures (>200 MPa) andtemperatures (>2000° C.). Powdered metal carbide precursor fabricationrequires independent synthesis from metal particles, salts, oxides, andcarbon (graphite or amorphous carbon) in a reducing hydrogen atmosphereat high temperatures (>2000° C.) to ensure high conversion to powderedmetal carbides. Metal nitrides require spark plasma sintering,high-temperature autoclave treatment of polymers or metal salts, orreduction-nitridation of metal oxides. These processes are allexpensive, energy-demanding, and difficult to scale up for industrialproduction. Sintered refractory ceramics exhibit grain coarsening andgranularity of individual agglomerated particles, which embrittles thesematerials. Therefore, there is a need for a previously undevelopedcost-effective method that yields metal carbides and metal nitrides withhigh purities and customizable properties.

The synthesis method uses a two-step process. The first step mixestogether the precursor composition that contains the followingingredients: (1) metal sources (metal powder and/or metal hydridemicro/nanopowder, such as W, Ti/TiH₂, B, and Zr/ZrH₂); (2) meltableacetylenic-containing aromatic polymeric resin that contains solelycarbon and hydrogen atoms; and (3) a nitrogen-rich polymeric resin thatdecomposes under high temperatures (optional). These precursors arepulverized/blended together for extended periods of time using a ballmill for a prescribed length of time. The various milled/powderedrefractory metal-carbon based resin precursor compositions are,subsequently, thermally converted to the final ceramic using a two stageprocess. Stage 1 yields a powdered or monolithic metal carbide or metalnitride compositions, while stage 2 yields monolithic metal-nitride andmetal carbide-carbon matrix compositions. Both stages involvepressureless heating of the powder (in a crucible or boat) or pressedthermoset/ceramic shape in a tube furnace up to 1500° C. under flowingnitrogen or argon atmospheres. Stage 1 yields pure metal carbides ormetal nitrides and can be processed further, including oxidative removalof any excess carbon or pulverization into a fine ceramic powder. Stage2 of the thermal treatment step involves milling of powdered metalnitrides and/or metal carbides (from stage 1) with small amounts of thepolymeric resin, cold-pressing of resulting powder into shapes withvariable form factors and dimensions, and thermally converting them toshaped ceramics using identical conditions as stage 1. In essence, theceramic nanoparticles or nanocrystallites formed in step 1 are mixedwith very small amounts of the carbon polymeric resin precursor, whichacts as a binder and retains the ceramic particles in a matrix duringits conversion to a thermoset. The two-stage heating process physicallycontrols the ultimate ceramic size within the confines of the shapedthermoset, which is thermally converted into metal carbide or nitridemonoliths.

Another aspect concerns formulations of carbon-fiber reinforcedrefractory metal carbide carbon-matrix composites. As an additionalstructural reinforcement process, carbon fibers are incorporated intovarious mixtures of precursor compositions that include pure metal/metalhydride powders (from Groups III-VI) and the meltable acetylenic-basedpolymer resins, which act as the sources of carbon. For metal nitridesynthesis, a nitrogen-rich polymer resin is also incorporated into themixture. The precursor powdered ceramic compositions (pure powderedceramics and carbon precursor), which are described in step 1 above, aremixed with continuous carbon fibers or chopped carbon fibers, pressedinto various shapes with different dimensions, and heated untilconversion into shaped thermoset forms. The fiber-containing mixture isconverted into a shaped thermoset solid at temperatures below 500° C. Itis subsequently heated up to 1000-1500° C. and yields a carbonfiber-reinforced metal ceramic matrix composite. Heating in an inertatmosphere (argon) promotes synthesis of carbon fiber-reinforcedrefractory metal carbide-carbon matrix composites, while heating in anitrogen atmosphere promotes synthesis of carbon fiber-reinforcedrefractory metal nitride-carbon matrix composites. Depending on thespecific chemistry of the resulting ceramic, the tough, solid shapedcomposite can be used for structural applications and at temperaturesthat exceed 3000° C. The precursor compositions can contain acombination of different refractory metal compounds that will lead to amixture of ceramics in the composite, which could be beneficial forspecific applications.

Both approaches include two main factors. The first factor incorporatesa nitrogen-rich polymer (with only carbon, hydrogen, and nitrogen atoms)that decomposes into nitrogen-containing compounds at high temperatureand reacts with the adjacent metal atoms in the milled mixture to formmetal nitrides. This yields a final dense ceramic that, instead of acarbide core and a nitride shell, features uniform metal nitridecomposition throughout the matrix. The second factor employs smallamounts of the acetylenic-based polymer resin as a binder that densifiesindividual metal carbide and/or metal nitride particles duringcold-pressing, retains them in a thermoset during heating up to 500° C.,and converts to a carbon-ceramic matrix during heating up to 1500° C.This approach yields customizable dense metal carbides and/or nitridesfrom any metal ceramic powder without hot press sintering. Thecomposites will have outstanding oxidative stabilities, tunableelectrical and thermal conductivities, high densities and mechanicalhardness, and melting temperatures that exceed 3000° C.

This approach, which can assemble WC nanoparticles into a matrix that isbound together with a carbon-based thermoset, yields continuousmonoliths with tunable surface areas. Subsequently, this method may beused to manufacture nanostructured metal carbide catalysts forelectrochemical energy storage, generation, and conversion.

A method has been developed to produce refractory metal (Ti, W, Nb, Zr,Mo, Cr, V, Ta, and Hf) carbides and nitrides in powdered and shapedsolid configurations from milled precursor compositions. Precursormaterial mixtures, which are initially in powder form and can eitherremain powders or be cold-pressed into various shapes, contain puremetals or metal hydrides that are embedded in carbon-rich (and,optionally, nitrogen-rich) polymer resins. The ceramics are produced asnanoparticles, microparticles, or dense shapes with nanocrystallinedomains.

The procedure employs a two-step process. The first step combines a)metal particles or metal hydrides (which desorb hydrogen at hightemperatures and convert to similar metal particles) with b) carbonprecursors that melt and contain only carbon and hydrogen as a powdercomposition and, optionally, with c) nitrogen-rich polymer resins thatcontain only carbon, nitrogen, and hydrogen and decompose at hightemperatures. The carbon sources are melt-processablearomatic-containing acetylenes or low molecular weight polymers thatexhibit extremely high char yields. The carbon precursor contains only Cand H to insure that heteroatoms are not incorporated into theinterstitial sites of the metal nanoparticles during the reaction toproduce the nanocrystalline metal carbide and/or metal nitride attemperatures up to 1500° C. under inert atmospheres. If used, thenitrogen-rich polymer decomposes into hydrocarbons, ammonia gas,nitrogen gas, and other similar light molecules. The initial compositionis milled and thermally converted to d) a stable thermoset withmetal/metal hydride particles embedded in a rigid polymer matrix. Themetal carbides or metal nitrides form between 600-1000° C. under inertconditions from reaction of the highly reactive metal particles witheither the carbon precursor (degradation above 500° C.) or nitrogen gas,respectively, but the reaction can be made to occur faster at highertemperatures. Further thermal treatment under argon or nitrogenatmospheres converts the powdered composition into e) metal carbides ormetal nitrides embedded in a carbon matrix. The appropriate pure metalpowders react directly with the carbon in the acetylenic resin, whilemetal hydride particles first undergo in situ transformation into metalparticles by thermally decomposing metal hydrides into metal andhydrogen gas. If used, nitrogen-rich polymer decomposes at temperaturesbelow 800° C., and resulting nitrogen compounds react with both thepolymer resin and the metal particles to yield metal nitrides. Allenveloping carbon may be removed by oxidative (air) thermal exposure ofthe powdered mixture, which leaves solely metal carbide or metal nitridenanoparticles with nanocrystalline domains.

In the second step, the pure monocrystalline ceramic produced in step 1is mixed with additional carbon resin (<10 wt. %) and milled for anextended period. The milled composition is then consolidated to shapeunder pressure and then heated up to about 300° C. under either nitrogenor argon, respectively, producing the shaped thermoset-containingceramics. Further heating of the thermoset-containing ceramics up to1000° C. affords high-density metal nitride or metal carbide compositesthat are enveloped by a thick carbon matrix. The composites retain theshape of the initially machined shaped ceramic-carbon resin precursors.In this step, the role of the polymer resin is to bind the ceramicparticles together, facilitate their densification at high temperatures,and maintain a stable, rigid thermoset matrix that holds the particlesin place and converts to a carbon-containing composite. As it chars, thepolymer does not affect the chemistry of the already-formed metalceramics but, instead, forms a nanostructured or amorphous elasticcarbon and improves the density and structural integrity of theresulting monoliths.

The method (FIG. 1) starts with a metal component, an organic compound,and optionally a nitrogenous compound. The initial components may alsooptionally comprise fibers, carbon fibers, ceramic fibers, or metalfibers.

The metal component may be nanoparticles or particles of a refractorymetal or a refractory metal hydride. The refractory metals may includetitanium, tungsten, niobium, zirconium, molybdenum, chromium, vanadium,tantalum, and hafnium. One suitable metal component is zirconiumhydride.

The organic compound consists of only carbon and hydrogen atoms, such as1,2,4,5-tetrakis(phenylethynyl)benzene (TPEB) or a prepolymer thereof.Other phenylethynyl benzene compounds are also suitable.

The nitrogenous compound consists of only carbon, nitrogen, and hydrogenatoms. One suitable compound is 1,3,5-triazine-2,4,6-triamine or aprepolymer thereof.

The initial components are combined, milled, and heated in an inertatmosphere such as nitrogen or argon. The heating is performed at atemperature that causes organic compound to polymerize to a thermoset.The heating may also cause decomposition or reaction of the metalcomponent to form nanoparticles. In this step, a metal hydride maydecompose to form metal nanoparticles. The metal particles 10 would thenbe dispersed throughout the thermoset 20 as shown in FIG. 2. The curedcomposition is then milled a second time.

In a second heating step, the cured, milled composition is heated in aninert atmosphere, argon, or nitrogen at a temperature that causesformation of a ceramic comprising metal carbide and optionally metalnitride in a carbonaceous matrix. The ceramic may be in the form of apowder. FIG. 3 schematically illustrates the transfer 40 of carbon atomsfrom the carbon matrix 30 to the nanoparticle 50.

At this point, the powder may be heated in an oxidizing atmosphere toremove any remaining organic material. The powder is then combined withadditional TPEB or other organic compound or polymer resin and milledagain. This result is heated in an inert atmosphere, argon, or nitrogenat a temperature that causes formation of a ceramic comprising thecarbide of the refractory metal and optionally the nitride of therefractory metal. This heating may be performed in a mold to form ashaped article.

FIG. 4 schematically illustrates nanoparticles 50 and inclusions 60 in acarbonaceous matrix 70. Example heating steps and precursor materialsare disclosed in U.S. Pat. Nos. 8,822,023; 8,865,301; 8,815,381;8,778,488; and 10,189,747.

The nanoparticles in the ceramic may be for example, zirconium carbideor zirconium nitride. The ceramic may comprise, for example, at least5%, 10%, 50%, 90%, 95%, or 99% by weight of the nanoparticles and/orfiller. The balance of carbonaceous matrix may be a small amountsufficient to adhere the nanoparticles together.

The methods may be summarized as follows. Step 1: powdered metal ormetal hydride+nitrogen-rich polymer (optional)→precursorcomposition+milling→cure to thermoset→milling of thermoset topowder→heat to 1500° C. in either nitrogen (metal nitrides) or argon(metal carbides)→heat powdered ceramics in oxygen (remove excess carbon)(optional)→either pure metal nitride or metal carbide. Step 2: puremetal nitride or metal carbide+minute quantity of TPEB+milling→heat andcure to shaped thermoset→heat to shaped metal nitride or metal carbideembedded in minute quantity of carbon.

The milling of the precursor compositions in step 1 may reduce the metalparticle size and activate its reaction with the carbon source, therebylowering the temperature of metal carbide or metal nitride formation.Moreover, by varying the amount of metal compound that forms reactivemetal particles relative to the polymer resin in step two, the amount ofmetal carbide or metal nitride within the final shaped ceramiccomposition can be changed with respect to the amount of carbon matrixin order to vary the properties of the resulting composition. Themetal-carbide or metal nitride carbon-matrix compositions are expectedto show enhanced toughness, owing to the presence of the relativelyelastic carbon, which would exist in forms ranging from amorphous tonanotube to graphitic carbon.

Potential advantages and features of the disclosed products and methodsinclude the following.

The method provides high-purity, high-yield synthesis of pure refractorynanoparticle metal nitrides or metal carbide ceramics withnanocrystalline domains in powdered and shaped forms from a reaction ofa meltable polymeric resin with the appropriate metal powder or metalhydride powder and a nitrogen-rich polymer.

The method provides formation of either shaped refractory nanoparticlemetal nitrides or metal carbides with nanocrystalline domains in atwo-step method.

Regardless of the ratio of metal source to carbon source, the metalcarbides or nitrides form as nanoparticles with nanocrystalline domains:this is a highly desirable result, as it is generally accepted thathomogeneous nanocrystalline composites of ceramics will have betterproperties than their (more common) microparticle-based counterparts.

The synthetic process occurs under no applied pressure and at much lowertemperatures than conventional synthesis and densification sinteringmethods for carbide and nitride ceramics.

By its very nature, the method improves facile customization of carbideor nitride and carbide- or nitride-carbon composites by liquid moldingprocedures (injection molding, vacuum molding, spreading, etc.), whichis a far less costly and involved process than machining a hot presssintered material.

The native presence of an “elastic” carbon matrix allows for tougheningof the inherently brittle ceramics. The carbon permits operation of thetoughened ceramic at extremely high temperatures, owing to carbon's highmelting point (>3000° C.). Ceramic/carbon-matrix compositions arecurrently sought for these reasons, and the present method permitsstraightforward preparation of these composites in a single step for thefirst time, in contrast to the traditional means of first forming theceramic powder and then preparing the carbon-matrix composite undersintering conditions. Also, the ratio of ceramic to carbon is easilytuned based only on the ratio of metal-compound to carbon-precursor.

Step 2 of the process is versatile and can be applied to any carbide ornitride, regardless of whether it was synthesized using the step 1method or using other means. It can incorporate other non-ceramicfillers, such as carbon reinforcements, metal inclusions, glass fibers,etc. It can be extrapolated and applied to borides, oxides, silicides,and other high-temperature refractory materials.

Carbon fiber-reinforced refractory metal carbide and metal nitridecarbon matrix composites produced from the precursor compositions ofstep 1 and 2 may exhibit outstanding mechanical properties. They mayoffer superior performance under extreme conditions such as hightemperatures, oxidative/ablative environments, and mechanical andthermal shock and repetitive stresses; such materials do not currentlyexist. Finely divided fiber-reinforced refractory nanoceramic carboncomposites allow the consolidation of fully dense shaped solidcomponents with extreme fracture resistance for uses in high stress andtemperature applications. Examples include advanced engine componentsand automobiles, where increased operation temperature and mechanicalintegrity could translate into tremendous economic advantages. Suchtough, easily shaped ceramic composites are critical to the nextgeneration of jet engines, which are being designed to operate at higherinternal temperatures and stresses than those in current service, and inadvanced automobile engines and supporting components. The rails of arailgun would be improved with hard, high-temperature, conductiveceramic coatings. The materials could be used as tough, high temperatureinsulators and in the design of hard, conductive rails with superiorwearability (no grooving). Metal nitrides show tunable electronicproperties and, coupled with their high temperature stability andmechanical hardness, may find use in high-temperature electronics. Inaddition, these materials can be fabricated into high temperature shipdeck plates for aircraft carriers, which require high toughness andsuperior heat-resistant composites. Lightweight, tough, and hardceramics molded in shaped structures are in high demand for superiormilitary armor (XSAPI and ESAPI plates) components. Such materials couldprovide vehicle and personnel protection against emerging ballisticthreats, such as tungsten carbide-based armor-piercing rounds.Conversely, these materials may serve as kinetic projectiles and eitherimprove the penetration capability or ablation resistance (crucial forrailgun warheads) of new ammunition. The ability to fabricate pure,tough, and shaped refractory metal carbides or metal nitride componentsin two steps improves their economic viabilities and missioncapabilities of a broad array of military systems.

As a proof-of-concept example, this procedure was applied to synthesizezirconium nitride (ZrN) from a mixture of Zr metal precursors (Zr andZrH₂), an acetylenic resin, and a nitrogen-rich resin. The structure ofthe material after step 1, as derived from Zr and ZrH₂, is shown in theX-ray diffraction plot in FIG. 5. The structure of the material, asderived from ZrH₂, after step 2 is shown in the XRD plot in FIG. 6.

The following examples are given to illustrate specific applications.These specific examples are not intended to limit the scope of thedisclosure in this application.

Example 1

Zirconium Nitride/Zirconium Carbonitride—Zirconium nitride (ZrN) andzirconium carbonitride (ZrC_(0.5)N_(0.5)) were synthesized from blendsof zirconium metal (Zr) and TPEB. Alternatively, ZrN andZrC_(0.5)N_(0.5) composites were synthesized from blends of zirconiumhydride (ZrH₂) and TPEB. Zr was blended together with TPEB for a ratioof 6.8 g of Zr per 1.0 gram of TPEB, and ZrH₂ was blended together withTPEB for a ratio of 6.4 g of ZrH₂ per 1.0 gram of TPEB. The twomaterials were blended together in a steel ball mill with steel grindingmedia and used nitrogen gas (N₂) or methylene chloride (CH₂Cl₂) organicliquid as the media that filled the void space between grinding mediaand metal and polymer particles. The blended materials were compactedinto discs and heated in a tube furnace under flowing N₂ gas up to 1400°C. Table 1 summarizes the resulting densities of this material.

TABLE 1 Disk Volumetric Archimedes′ Zirconium Grinding Mass WidthThickness Volume Density Density Precursor Media (g) (mm) (mm) (cm³)(g/cm³) (g/cm³) Zr N₂ 0.89 13.00 1.98 0.26 3.38 4.48 CH₂Cl₂ 0.86 13.001.51 0.20 4.31 4.58 ZrH₂ N₂ 0.88 13.00 1.72 0.23 3.86 4.45 CH₂Cl₂ 0.8713.00 1.54 0.20 4.24 4.67

Visual inspection of the precursor powders and final ceramic discsshowed that the initial powder mixtures retained dark-brown/grey/blackcolors (characteristic of bulk TPEB, Zr, and ZrH₂ particulatematerials). Finalized samples were dense disks with darkyellow/golden/light-brown colors, which are typical for bulk ZrNmaterials.

X-ray diffraction analysis analyzed the crystal structure of theresulting composition. It is shown in FIG. 5. Composition analysisshowed that resulting material was composed of predominantly zirconiumnitride and zirconium carbonitride. The sample was devoid of anynoticeable zirconium carbide (ZrC) phase. Some metal oxide (ZrO₂)material was present due to minimal surface oxidation of individualparticles or overall disks as a result of exposure to oxygen postsynthesis or trace amounts of oxygen during high-temperature processing.Table 2 shows the Rietveld analysis of the X-ray diffraction data.

TABLE 2 Zirconium Resulting Lattice Parameter Precursor Phase Weight %(nm) Zr ZrC_(0.5)N_(0.5) 98.7 33.9 ZrO₂ 1.2 68.5 ZrH₂ ZrN 50.7 22.5ZrC_(0.5)N_(0.5) 46.5 19.8 ZrO₂ 2.8 21

The reaction profiles (up to 1000° C.) of the blend of ZrH₂ and TPEBwere analyzed using thermogravimetric analysis with a differentialscanning calorimetry component (TGA-DSC). The test conditions resembledthermal treatments of the samples in nitrogen in a tube furnace. FIG. 6shows the mass change of the materials as a function of temperature.

Scanning electron microscopy (SEM) imaging analyzed the morphology ofparticles formed during the reaction of ZrH₂ and TPEB under flowing N₂.The formed ZrN/ZrC_(0.5)N_(0.5) particles were small (0.5-10 micrometersin diameter) and bound together on fractions of their edges. Themorphology analysis reveals a uniform and homogeneous composition.

Example 2

Zirconium Nitride Two-Step Synthesis Composite—Zirconium nitride (ZrN)ceramic monoliths were synthesized via a two-step approach. In the firststep, three-ingredient blends of ZrH₂, TPEB, and melamine (C₃H₆N₆), aswell as three-ingredient blends of Zr, TPEB, and melamine were preparedusing ball milling. N₂ gas, hexane (C₆H₁₄) fluid, and CH₂Cl₂ fluid wereused to fill the void space between grinding media and sample particles.For materials that used Zr, the precursor blend included 3.06 g Zr; 0.46g TPEB; and 0.69 g melamine. For materials that used ZrH₂, the precursorblend included 6.00 g ZrH₂; 0.71 g TPEB; and 1.38 g melamine. The groundparticle blends were placed in a tube furnace (as a powder poured into aceramic boat or compacted into a cold-pressed disc). These materialswere heated up to 1400° C. under flowing N₂. The resulting material is azirconium nitride powder. In the second step, the ZrN (hereafterreferred to as “bulk ZrN”) synthesized from the first step was blendedtogether with mixtures of ZrH₂ and TPEB (hereafter referred to as “ZrNbinder”). The ZrN binder was composed of 0.15 g TPEB per 1.00 g of ZrH₂,The ratio of bulk ZrN to ZrN binder was 9.0 grams of bulk ZrN per 1.0grams of ZrN binder. The constituents were milled together usingball-milling. The resulting precursor powders were compacted into discsand heated up to 1400° C. in flowing N₂ gas. Table 3 summarizes theresulting densities of materials synthesized from ZrH₂.

TABLE 3 Disk Volumetric Num- Zirconium Mass Width Thickness VolumeDensity ber Precursor (g) (mm) (mm) (cm³) (g/cm³) 1 ZrCN—ZrH₂ 6.469 25.24.18 2.08 3.10

XRD analysis of the ZrN powder (synthesized in the first step) and theZrN ceramic (synthesized in the second step) showed that the crystalstructure was identical for the two materials. The data is shown in FIG.8. Table 4 summarizes the crystal properties and relative compositionsof the phases that are present in the material.

TABLE 4 Synthesis Lattice Parameter Stage Phase Weight % (nm) Phase 1ZrN_(0.92) 95.5 23.5 ZrO₂ 1.7 16.3 Zr 2.8 101.5 Phase 2 ZrN 99.1 23.2ZrO₂ 0.9 28.6

Samples synthesized using the two-step method show a distinctyellow-gray color that is characteristic of bulk zirconium nitride. FIG.9 shows a photo of a disc prepared using the two-step synthesisapproach.

Example 3

Zirconium Nitride Formed Using Nitrogen-Rich Polymer Precursor—Zirconiumnitride (ZrN) ceramic monoliths were synthesized via a two-stepapproach. In the first step, two-ingredient blends of ZrH₂ and1,3,5-triazine-2,4,6-triamine (hereafter referred to as “TAM”) wereprepared using ball milling. N₂ gas, hexane (C₆H₁₄) fluid, and CH₂Cl₂fluid were used to fill the void space between grinding media and sampleparticles. The precursor blend was composed of 4.267 g ZrH₂ and 0.639 gTAM. The blended powder was placed in an alumina crucible and heated ina tube furnace under flowing N₂ gas up to 1,450° C. The synthesisyielded ZrN powder. The second synthesis step blended together 4.267 gof ZrN and 0.639 grams of TAM using ball-milling. The blended powder wascompacted into a disc and heated in a tube furnace under flowing N₂ gasup to 1,450° C.

FIG. 10 shows a photograph of the resulting monolith. As revealed withXRD analyses, the resulting disc was composed of ZrN. FIG. 11 shows theXRD data from the disc.

Example 4

Zirconium Nitride Formed Using Nitrogen-Rich Polymer Precursor—Zirconiumnitride (ZrN) ceramic monoliths were synthesized via a single-stepapproach. ZrH₂ (4.269 g), TPEB (0.159 g), and TAM (0.479 g) were blendedtogether using ball-milling (in CH₂Cl₂ fluid with stainless steelgrinding media). The blended powder mixture was compacted into discsusing a hydraulic press while being heated up to 220° C. The disc wastreated in a tube furnace with flowing N₂ gas at 1450° C. The resultingmaterial was a rigid ceramic monolith composed of ZrN.

Example 5

Boron Nitride Formed Using Melamine and a Polymer Resin—Boron nitride(BN) composite ceramic monoliths were synthesized via a single-stepapproach. Boron (2.5 g), TPEB (9.727 g), and melamine (3.125 g) wereblended together using ball-milling in an N₂ environment. The materialwas compacted into a 25 mm diameter disc and treated in a tube furnacewith flowing N₂ gas at 1450° C. FIG. 12 shows a thermal analysis of asample of the mixture treated in a TGA instrument using the sameconditions. The resulting structure, as determined with XRD analysisshown in FIG. 13, is a blend of hexagonal boron nitride, with smallfractions of boron carbide and graphite.

Scanning electron microscopy (SEM) imaging analyzed the morphology ofsurface of composite formed during the reaction of Boron, TPEB, andmelamine under flowing N₂. FIG. 14 shows the microscopy analysis. Themorphology analysis reveals a uniform layer surface and homogeneouscomposition.

Example 6

Titanium Nitride Formed Using Melamine and a Polymer Resin—Titaniumnitride (TiN) composite ceramic monoliths were synthesized via asingle-step approach. Titanium (3.00 g), TPEB (0.79 g), and melamine(1.34 g) were blended together using ball-milling in an N₂ environment.The material was compacted into a disc and treated in a tube furnacewith flowing N₂ gas at 1450° C.

Example 7

Vanadium Nitride Formed Using Melamine and a Polymer Resin—Vanadiumnitride (VN) composite ceramic monoliths were synthesized via asingle-step approach. Vanadium (3.00 g), TPEB (0.32 g), and melamine(1.26 g) were blended together using ball-milling in an N₂ environment.The material was compacted into a disc and treated in a tube furnacewith flowing N₂ gas at 1450° C.

Example 8

Tantalum Nitride Formed Using Melamine and a Polymer Resin—Tantalumnitride (TaN) composite ceramic monoliths were synthesized via asingle-step approach. Tantalum (3.00 g), TPEB (0.21 g), and melamine(0.36 g) were blended together using ball-milling in an N₂ environment.The material was compacted into a disc and treated in a tube furnacewith flowing N₂ gas at 1450° C.

Example 9

Tungsten Nitride Formed Using Melamine and a Polymer Resin—Tungstennitride (WN) composite ceramic monoliths were synthesized via asingle-step approach. Tungsten (3.00 g), TPEB (0.21 g), and melamine(0.35 g) were blended together using ball-milling in an N₂ environment.The material was compacted into a disc and treated in a tube furnacewith flowing N₂ gas at 1450° C.

Example 10

Silicon Nitride Formed Using a Blend of Two Polymer Resins—Siliconnitride (Si₃N₄) composite ceramic monoliths were synthesized via asingle-step approach. Silicon metal (4.00 g), TPEB (0.680 g), and TAM(2.04 g) were blended together using ball-milling in a CH₂Cl₂ fluidenvironment. The material was compacted into a disc and treated in atube furnace with flowing N₂ gas at 1450° C.

Scanning electron microscopy (SEM) imaging analyzed the morphology ofsurface of composite formed during the reaction of silicon, TPEB, andmelamine under flowing N₂. FIG. 15 shows the microscopy analysis. Themorphology analysis reveals a uniform layer surface and homogeneouscomposition.

XRD analysis confirmed the structure of the resulting ceramic monolith.FIG. 16 shows the XRD plot. The predominant phases were Si, SiC, andSi₃N₄.

Obviously, many modifications and variations are possible in light ofthe above teachings. It is therefore to be understood that the claimedsubject matter may be practiced otherwise than as specificallydescribed. Any reference to claim elements in the singular, e.g., usingthe articles “a”, “an”, “the”, or “said” is not construed as limitingthe element to the singular.

What is claimed is:
 1. A composition comprising: nanoparticles of arefractory-metal carbide, boron carbide, or silicon carbide; andnanoparticles of a refractory-metal nitride, boron nitride, or siliconnitride; wherein the composition has a uniform distribution of thecarbide and the nitride; wherein the composition is in the form of apowder.
 2. The composition of claim 1, wherein the nanoparticlescomprise zirconium carbide and zirconium nitride, boron carbide andboron nitride, silicon carbide and silicon nitride, titanium carbide andtitanium nitride, tantalum carbide and tantalum nitride, tungstencarbide and tungsten nitride, hafnium carbide and hafnium nitride, orvanadium carbide and vanadium nitride.
 3. The composition of claim 1,wherein the composition comprises at least 5% by weight of thenanoparticles.
 4. A method comprising: combining the composition ofclaim 1 with an organic compound consisting of carbon and hydrogen or apolymer resin to form a precursor composition; milling the precursormixture; and heating the precursor composition in an inert atmosphere,argon, or nitrogen at a temperature that causes formation of a ceramiccomprising the carbide, the nitride, and a carbonaceous matrix.
 5. Themethod of claim 4, wherein the organic compound is1,2,4,5-tetrakis(phenylethynyl)benzene or a prepolymer thereof.
 6. Thecomposition of claim 1, wherein the composition further comprises: acarbonaceous matrix.
 7. The composition of claim 1, wherein thecomposition further comprises: fibers, carbon fibers, ceramic fibers, ormetal fibers.
 8. A composition comprising: a metal component selectedfrom: nanoparticles or particles of a refractory metal, boron, silicon,a refractory metal hydride, a refractory metal carbide, boron carbide,silicon carbide, a refractory metal nitride, boron nitride, siliconnitride, and a refractory metal boride; an organic compound consistingof carbon and hydrogen; and a nitrogenous compound consisting of carbon,nitrogen, and hydrogen.
 9. The composition of claim 8, wherein the metalcomponent is zirconium hydride, titanium hydride, titanium, zirconium,tungsten, boron, silicon, tantalum, hafnium, or vanadium.
 10. Thecomposition of claim 8, wherein the organic compound is1,2,4,5-tetrakis(phenylethynyl)benzene or a prepolymer thereof.
 11. Thecomposition of claim 8, wherein the nitrogenous compound is1,3,5-triazine-2,4,6-triamine or a prepolymer thereof.
 12. Thecomposition of claim 8, wherein the composition further comprises:fibers, carbon fibers, ceramic fibers, or metal fibers.
 13. Thecomposition of claim 8, wherein the metal component is selected from:nanoparticles or particles of the refractory metal, the refractory metalhydride, the refractory metal carbide, the refractory metal nitride, andthe refractory metal boride.
 14. A method comprising: providing aprecursor composition comprising: a metal component selected from:nanoparticles or particles of a refractory metal, boron, silicon, or arefractory metal hydride; an organic compound consisting of carbon andhydrogen; and 1,3,5-triazine-2,4,6-triamine; milling the precursorcomposition; curing the precursor composition to form a thermosetcomposition; milling the thermoset composition; and heating thethermoset composition in an inert atmosphere at a temperature that formsa nanoparticle composition comprising nanoparticles of a carbide of therefractory metal, boron, or silicon and a nitride of the refractorymetal, boron, or silicon.
 15. The method of claim 14, wherein the metalcomponent is zirconium hydride.
 16. The method of claim 14, wherein theorganic compound is 1,2,4,5-tetrakis(phenylethynyl)benzene or aprepolymer thereof.
 17. The method of claim 14, further comprising:heating the nanoparticle composition in a oxidizing atmosphere to removeany organic material.
 18. The method of claim 14, further comprising:combining the nanoparticle composition with the organic compound or apolymer resin to form a second precursor composition; milling the secondprecursor composition and heating the second precursor composition in aninert atmosphere, argon, or nitrogen at a temperature that causesformation of a ceramic comprising the carbide of the refractory metal,boron, or silicon and the nitride of the refractory metal, boron, orsilicon.
 19. A method comprising: providing a composition comprising:nanoparticles of a refractory-metal carbide, boron carbide, or siliconcarbide; and optionally nanoparticles of a refractory-metal nitride,boron nitride, or silicon nitride; wherein the composition has a uniformdistribution of the carbide and optionally the nitride; combining thecomposition with an organic compound consisting of carbon and hydrogenor a polymer resin to form a precursor composition; milling theprecursor mixture; and heating the precursor composition in an inertatmosphere, argon, or nitrogen at a temperature that causes formation ofa ceramic comprising the carbide, optionally the nitride, and acarbonaceous matrix.
 20. The method of claim 19, wherein the organiccompound is 1,2,4,5-tetrakis(phenylethynyl)benzene or a prepolymerthereof.
 21. The method of claim 19, wherein the composition comprisesnanoparticles of the refractory-metal carbide and optionallynanoparticles of the refractory-metal nitride.
 22. A method comprising:providing a precursor composition comprising: a metal component selectedfrom: nanoparticles or particles of a refractory metal, boron, silicon,or a refractory metal hydride; an organic compound consisting of carbonand hydrogen; and a nitrogenous compound consisting of carbon, nitrogen,and hydrogen; milling the precursor composition; curing the precursorcomposition to form a thermoset composition; milling the thermosetcomposition; heating the thermoset composition in an inert atmosphere ata temperature that forms a nanoparticle composition comprisingnanoparticles of a carbide of the refractory metal, boron, or siliconand a nitride of the refractory metal, boron, or silicon; and heatingthe nanoparticle composition in a oxidizing atmosphere to remove anyorganic material.
 23. The method of claim 22, wherein the metalcomponent is zirconium hydride.
 24. The method of claim 22, wherein theorganic compound is 1,2,4,5-tetrakis(phenylethynyl)benzene or aprepolymer thereof.
 25. The method of claim 22, further comprising:combining the nanoparticle composition with the organic compound or apolymer resin to form a second precursor composition; milling the secondprecursor composition and heating the second precursor composition in aninert atmosphere, argon, or nitrogen at a temperature that causesformation of a ceramic comprising the carbide of the refractory metal,boron, or silicon and the nitride of the refractory metal, boron, orsilicon.